In the past few years, agriculture in the United States has been revolutionized by the introduction of transgenic crops that are resistant to specific diseases, insects, herbicides or have improved nutritional value. At the same time, much concern has been expressed around the world that these genetically modified (GM) agricultural products may be harmful to the consumer and that the transgenes could be transferred to related plant species so as to generate insect- or herbicide-resistant “superweeds” (Ferber, D., Science 286:1662 (1999)) or consumed by other organisms to their detriment (Losey, et al., Nature 399:214 (1999)). Whereas there is little scientific basis to the fear of harmful effects of “GM foods”, the possibility that transgenes are transferred to other plants and thereby have an adverse ecological impact is not entirely unfounded (Bergelson, et al., Nature 395:25 (1998)). Such transfer could occur either by pollination of closely related species or by the transfer of gene fragments to unrelated plants by viral or plasmid vectors whose transmission may be mediated by plant-associated fungi, bacteria or insects.
There have been a number of techniques discussed for the prevention of transgene spread, however these procedures either are designed to have a negative impact on the new hybrid plant (Gressel, Trends Biotechnol., 17:361-366 (1999)), as in the case of tandem constructs or will not eliminate the possiblity of spread by horizontal gene transfer (Bertolla and Simonet, Res. Microbiol., 150:375-384 (1999)).
In this disclosure, we propose a new type of transgene that allows efficient protein expression but does not require a gene coupling approach and has a significantly lower chance of spread by horizontal gene transfer.